JPH11297307A - Polymer lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make satisfactory applicability of a positive electrode mix and a negative electrode mix to a current collector and current collectability for making satisfactory battery performance. SOLUTION: An metal foil having 3 μm or more for surface roughness Rz in conformance with JIS-C-0601 is used as a current collector for a positive electrode and a negative electrode, in a polymer lithium ion secondary battery having the sheet-like positive electrode formed with a gelled positive electrode mix layer at least on one face of the current collector, a sheet-like negative electrode formed with a gelled negative electrode mix layer at least on one face of the current collector, and a polymer electrolyte layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer lithium ion secondary battery which is small, lightweight and thin.

[0002]

2. Description of the Related Art Conventionally, when an electrolyte is solidified, a battery free from liquid leakage can be obtained. Therefore, the battery has been regarded as the ultimate battery. However, the ion conductivity is several orders of magnitude lower than that of a solution type. Due to such problems, it was not possible to develop a versatile battery.

However, in recent years, when a polymer is gelled together with an organic solvent-based electrolyte, a polymer electrolyte having a high ionic conductivity and an improved ionic conductivity of about 10 ⁻³ S / cm can be obtained. By using this as an electrolyte for a battery, a battery having good characteristics has been obtained, and the polymer battery has come into the spotlight again.

[0004]

In such a polymer lithium ion secondary battery, electrodes such as a positive electrode and a negative electrode are formed by collecting a paste-like electrode mixture containing an active material, a binder, an electrolytic solution and the like into a current collector. It is manufactured by applying to the substrate and heating to form a gel-like electrode mixture layer, and a metal foil is used as the current collector. At this time, the electrode mixture adheres to the current collector. In order to improve the properties and applicability, mix a large amount of adhesive into the electrode mixture, or apply a conductive material such as acetylene black on the surface of the current collector in advance with an adhesive, An electrode mixture such as a positive electrode mixture or a negative electrode mixture has been applied thereon.

[0005] However, these operations lead to the introduction of an insulating adhesive into the battery, thereby inhibiting the battery reaction and causing one of the causes of deterioration in battery performance.

The present invention solves the above-mentioned problems of the prior art, and makes it possible to apply a positive electrode mixture or a negative electrode mixture to a current collector without using a large amount of an adhesive, thereby improving the battery performance. It is an object of the present invention to provide a polymer lithium-ion secondary battery having a good lithium ion secondary battery.

[0007]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, have found that a metal foil having a surface roughness Rz of 3 μm or more is used as a current collector for a positive electrode and a negative electrode. As a result, the above problems were solved, and the present invention was completed.

That is, in the present invention, in order to improve the adhesiveness and applicability of the positive electrode mixture and the negative electrode mixture to the current collector, the surface of the metal foil as the current collector is roughened, By increasing the contact area between the body and the positive electrode mixture or the negative electrode mixture, and exerting an anchor effect by its surface roughness, the adhesiveness or applicability of the positive electrode mixture or the negative electrode mixture to the current collector is improved. The above problem was solved by making it better.

[0009] For example, in the case of a copper-clad laminate, in order to enhance the effect of adhesion to a substrate such as polyimide, the surface of the copper foil is subjected to bumping treatment to increase the surface irregularities and increase the anchor effect. As a result, the peel strength is increased.

[0010] Since the positive electrode mixture and the negative electrode mixture in the polymer lithium ion secondary battery of the present invention are finally made into a gel, the adhesiveness to the current collector is as high as that of a copper-clad laminate. Since it is not very strong, it is sufficient to apply a positive electrode mixture or a negative electrode mixture on the surface of a normal metal foil (surface roughness Rz is usually about 0.6 μm) and heat it to gel it. Can not be obtained and easily peeled off. On the other hand, when a metal foil having a surface roughness Rz of 3 μm or more is used, the applicability of the positive electrode mixture and the negative electrode mixture to the metal foil is improved, and the positive electrode mixture and the negative electrode after gelation are used. Adhesion between the mixture and the current collector is improved, and peeling from the current collector is reduced. In the present invention, the surface roughness Rz is defined as JIS-C-060.
Refers to the surface roughness measured by the method specified in 1,
In this document, the case where “according to JIS-C-0601” is not particularly indicated also means the surface roughness Rz measured by the method specified in JIS-C-0601.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The surface roughness Rz of a metal foil used as a current collector is preferably as large as possible, and particularly preferably at least 5 μm. Further, the shape of the metal foil with the knob is preferably a shape in which the knob is mounted on the knob, and a metal foil having a complicated surface shape is more preferable. However, the surface roughness Rz
Is too large, it affects the strength of the metal foil. Therefore, when the surface roughness Rz is 3 μm or more and 16 μm
Hereinafter, those having a thickness of up to about 10 μm are particularly preferred.

As a method for increasing the surface roughness Rz of the metal foil, various methods such as a method of forming a bump by electrolysis, a method of roughening the surface by buffing, and a method of etching the surface by chemicals are employed. can do.

Examples of the material of the metal foil serving as the current collector include aluminum, copper, nickel, stainless steel, and graphite. The current collector of the positive electrode is preferably an aluminum foil, and the current collector of the negative electrode is preferably used. The body is preferably a copper foil.

[0014]

Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to only these examples.

Example for Positive Electrode To 10 g of LiCoO _{2 as a} positive electrode active material, ₂ g of acetylene black as a conductive material, 6 g of an electrolytic solution containing propylene carbonate as an electrolytic solvent and 1.2 g of polyvinylidene fluoride were added and mixed. A paste-like positive electrode mixture was prepared. The electrolytic solution was prepared by mixing LiPF _{6 in} a mixed solvent of propylene carbonate and ethylene carbonate at a volume ratio of 1: 1.
Was dissolved in 1.22 mol / l.

The paste-like positive electrode mixture is treated with a surface roughness Rz.
Are 0.6 μm, 3.0 μm, 7.4 μm, 1
It was applied to one surface of a 0.5 μm aluminum foil (the surface roughness of this surface was the above value) using an application machine. Table 1 shows the application status (at the time of application and after application).
Shown in The surface roughness Rz value of the aluminum foil is a value measured by a method specified in JIS-C-0601. In addition, the battery performance when the above-mentioned one was heated and gelled to be used as a positive electrode was examined. The results are also shown in Table 1. In the battery, the sheet-shaped positive electrode, 6 g of coke as the negative electrode active material, 0.6 g of acetylene black as a conductive material, 5 g of an electrolyte containing the same propylene carbonate as that used for the positive electrode as an electrolyte solvent, and polyfluoride were used. 0.8 g of vinylidene is added and mixed to prepare a paste-like negative electrode mixture, and the paste-like negative electrode mixture is applied to one surface of a copper foil having a surface roughness of 8.2 μm, and heated. A sheet-shaped negative electrode obtained by gelling, an acrylic monomer mixture composed of tri (ethylene glycol) dimethacrylate, ethylene glycol ethyl carbonate methacrylate and 2-ethoxyacrylate, and benzoyl peroxide and propylene as polymerization initiators thereof A mixture of the same electrolytic solutions containing carbonate as an electrolytic solvent is heated to overlap the monomers. Are those formed by combining the obtained sheet-shaped gel electrolyte by gelling with is, the comparison of the cell performance, 20 ° C., 4.2 V in CCCV at 0.5C
Charge at 0.5C and discharge to 2.75V at CV,
This was done by comparing the cycle characteristics.

[0017]

[Table 1]

Example of a negative electrode An electrolytic solution containing 6 g of coke as a negative electrode active material, 0.6 g of acetylene black as a conductive material, and propylene carbonate similar to that used for the positive electrode as an electrolyte solvent was used. 5 g of liquid and polyvinylidene fluoride 0.
8 g was added and mixed to prepare a paste-like negative electrode mixture.

The paste-like negative electrode mixture has a surface roughness Rz of 0.6 μm, 3.1 μm, 8.2 μm, and 12.
It was applied to one surface of a 2 μm copper foil (the surface roughness of this surface was the above value) using an application machine. Table 2 shows the application status (at the time of application and after the application). In addition,
The surface roughness Rz value of the copper foil is a value measured by a method specified in JIS-C0601. Further, the battery performance was examined when the above-mentioned battery was heated and gelled to be used as a negative electrode. The results are also shown in Table 2. The battery is made of the above sheet-shaped negative electrode and LiCoO which is a positive electrode active material.
_{2 To} 10 g, ₂ g of acetylene black as a conductive material, 6 g of the same electrolytic solution containing propylene carbonate as an electrolytic solvent and 1.2 g of polyvinylidene fluoride were added and mixed to prepare a paste-like positive electrode mixture. This paste-like positive electrode mixture is applied to one surface of an aluminum foil having a surface roughness of 7.4 μm, and heated to gel, and a sheet-like positive electrode is obtained. Acrylic monomer mixture consisting of methacrylate, ethylene glycol ethyl carbonate methacrylate and 2-ethoxy acrylate, and a mixture of the same electrolytic solution containing benzoyl peroxide and propylene carbonate as polymerization initiators as an electrolytic solution solvent are heated. A polymer obtained by polymerizing and gelling the monomer And a battery-like gel electrolyte in combination.
Charged to 4.2V by CCCV at 0.2 ° C and 0.2C, 0.5
This was performed by comparing the capacities after discharging to CV to 2.75 V with C and performing 10 cycles.

[0020]

[Table 2]

As is clear from the results shown in Tables 1 and 2, the use of a metal foil having a large surface roughness as a current collector allows a large amount of adhesive to be contained in the positive electrode mixture and the negative electrode mixture. It is possible to satisfactorily apply the positive electrode mixture and the negative electrode mixture without performing a pretreatment such as applying a conductive material to the surface of the metal foil with an adhesive beforehand, The battery manufactured using the foil as the current collector had good adhesion to the current collector, so that good battery performance was obtained.
As is apparent from this, according to the present invention, it is possible to stably produce a polymer lithium ion secondary battery having good battery performance.

[0022]

As described above, according to the present invention, the current collector of the positive electrode mixture and the negative electrode mixture can be obtained by using a metal foil having a surface roughness Rz of 3 μm or more as the current collector of the positive electrode and the negative electrode. It was possible to provide a polymer lithium ion secondary battery having good battery performance by making it possible to perform the coating on the battery well.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Eri Yokoyama 1-88 Ushitora, Ibaraki City, Osaka Prefecture Inside Hitachi Maxell Co., Ltd. (72) Inventor Taku Sugiyama 1-88 Ushitora, Ibaraki City, Osaka Prefecture Hitachi Maxell Co., Ltd. (72) Inventor Tetsuo Kawai 1-88 Ushitora, Ibaraki-shi, Osaka Hitachi Maxell Co., Ltd.

Claims (1)

[Claims] 1. A sheet-like positive electrode in which a gel-like positive electrode mixture layer is formed on at least one surface of a current collector, and a gel-like negative electrode mixture layer is formed on at least one surface of a current collector. In a polymer lithium ion secondary battery having a sheet-shaped negative electrode and a sheet-shaped polymer electrolyte layer, the current collector of the positive electrode and the negative electrode has a surface roughness Rz of 3 μm.
A polymer lithium ion secondary battery using the above metal foil.